import java.util.Arrays;

public class PriorityQueue {
    public int[] elem;
    public int usedSize;

    public PriorityQueue() {
        this.elem = new int[10];
    }

    /**
     * 建堆的时间复杂度：
     *
     * @param array
     */
    public void createHeap(int[] array) {
        for (int i = 0;i < array.length;i++){
            elem[i] = array[i];
            usedSize++;
        }
        for (int parent = (usedSize-1-1)/2;parent >= 0;parent--){
            shiftDown(parent,usedSize);
        }
    }

    /**
     *
     * @param parent 是每棵子树的根节点的下标
     * @param  end 是每棵子树调整结束的结束条件
     * 向下调整的时间复杂度：O(logn)
     */
    private void shiftDown(int parent,int end) {
        int child = 2*parent +1;
        while (parent<end){
            if(child + 1 < usedSize && elem[child] < elem[child+1]){
                child++;
            }
            if(elem[child] > elem[parent]){
                swap(child,parent);
                parent = child;
                child = 2*parent +1;

            }else {
                break;
            }
        }
    }
  private void swap(int i,int j){
        int tmp = elem[i];
        elem[i] = elem[j];
        elem[j] =tmp;
  }


    /**
     * 入队：仍然要保持是大根堆
     * @param val
     */
    public void push(int val) {
        if (isFull()){
            elem = Arrays.copyOf(elem,2*elem.length);
        }
        elem[usedSize] = val;
        usedSize++;
        shiftUp(usedSize-1);
    }

    private void shiftUp(int child) {
        int parent = (child-1)/2;
        while (child > 0){
            if (elem[child] > elem[parent]){
                swap(child,parent);
                child = parent;
                parent = (child-1)/2;
            }else{
                break;
            }
        }


    }

    public boolean isFull() {
        return  usedSize == elem.length;
    }

    /**
     * 出队【删除】：每次删除的都是优先级高的元素
     * 仍然要保持是大根堆
     */
    public int pollHeap() {

        int tmp = elem[0];
        swap(0,usedSize-1);
        usedSize--;
        shiftDown(0,usedSize);
        return  tmp;
    }

    public boolean isEmpty() {
        return usedSize > 0;
    }

    /**
     * 获取堆顶元素
     * @return
     */
    public int peekHeap() {
        return elem[0];
    }
}